Board holding devices have long been used in electronic equipment in which certain circuit components, combined to form sub-assemblies, are located on a number of printed circuit boards and retained so as to be exchangeable. The frame parts, which are generally manufactured from an insulating plastic, have grooves in their longitudinal direction. The grooves are matched to the dimensions of the printed circuit board in such a way that the board can be inserted without difficulty from the front and can also be withdrawn again. Multiple contact strips are often attached transversely to the groove direction at the rear end of the frame parts, into which multiple contact strips corresponding devices on the printed circuit board are inserted automatically when the board is pushed in, making the necessary electrical connections to other circuit components.
Whereas the frame parts described only represent mechanically effective holders with no electrical duty, it is often essential in the case of circuits which are exceptionally sensitive to interference or, for example, high-frequency circuits, to accommodate the printed circuit boards in a screening metal casing which is in good conductive connection with the ground conductor of the circuit, and to modify the holding devices in a suitable manner. In particular, however, it is increasingly important, in the case of very high operating frequencies in the GHz range, so to design the casing geometry that the desired high frequency properties are obtained in conjunction with the printed circuit board and its circuit. This leads to the construction of casings, manufactured to a large extent in advance, often milled or bent from sheet metal and soldered together, in which casings the printed circuit boards are subsequently inserted and then fastened.
This type of casing construction is, firstly, very expensive to manufacture. Secondly, however, it provides problems in producing an electrically reliable, large-area ground contact between the circuit and the screen subsequent to the installation of the board.